[Speaker 1]
Tomoko Suzuki, D3, Sokendai, Mitaka (supervisor : Tadayuki Kodama)
[Title]
Star-forming activity before the peak epoch as revealed by the NB-selected [OIII] emitters
[Abstract]
We have been constructing the sample of [OIII] emitters at z > 3 in order to investigate the galaxy formation before the peak epoch (z~2).
I will talk about the usefulness of the [OIII] emission line as a tracer of star-forming galaxies at high redshift, and then, introduce our work about the star-forming activity of the [OIII] emitters at z > 3.

[Speaker 2]
Rhythm Shimakawa, D3, Sokendai, Mitaka (supervisor : Tadayuki Kodama)
[Title]
First direct evidence of Lyα depletion in overdensities at z=2.5
[Abstract]
Galaxy protoclsuters (Sunyaev & Zeldovich 1972) at the peak epoch of cosmic star formation
(z=2?3) are ideal test-beds to characterise how cluster galaxies have been formed through cosmic mass assembly histories in large-scale structures (White & Frenk, 1991).
We carried out Lyα and Hα line imaging of the USS 1558 protocluster with Subaru telescope.
The wide field of view of the S-cam newly find large-scale structures of Lyα emitters (LAEs) in and around the protocluster discovered by Hα imaging with MOIRCS. However, we do not see an excess of number density in (LAEs) in the densest groups of Hα emitters (HAEs). Rather, LAEs are spatially distributed as if they are trying to avoid the densest groups that make up roughly half of the dense protocluster region. Composite line images of HAEs divided into two samples by their mean distance indicate the lower escape fraction of Lyα photons in the denser 25th percentiles of the HAE samples, suggesting that rich CGM/IGM matters deplete Lyα emission from star-forming galaxies in the overdense groups in USS 1558 (RS et al. to be submitted).
Combined with another new result we found (RS et al. in prep.), this first result would support “cold mode stream” scenario in massive structures (Dekel et al.
2009a,b). Moreover, our result
strongly cautions all past high-z protocluster surveys using Lyα line as galaxy tracer, which should be tracing more likely galaxies in “outskirts” not in main bodies within large-scale structures.